Pekka Punttila

Coarse woody debris and stand characteristics in mature managed and old-growth boreal mesic forests in southern Finland

Abstract Stand structure was studied on thirty 1-ha plots in mature managed and old-growth forest stands dominated by Norway spruce ( Picea abies L. Karst.) in southern Finland. The forests were classified into three categories (10 plots in each category) according to the age of the dominant spruces and signs of previous cutting: (1) mature managed (95–118 years), (2) overmature managed (124–145 years) and (3) old-growth (129–198 years). The average volume of the living trees was 299xa0m 3 /ha in mature, 331xa0m 3 /ha in overmature and 396xa0m 3 /ha in old-growth stands. The clearest difference in the living stand characteristics between the categories was in the numbers of large pines ( Pinus sylvestris L.) and deciduous trees, which were both ca. 10 times more frequent in old-growth than in mature stands, and intermediate in overmature stands. The average volume of coarse woody debris (CWD) with a minimum diameter of 5xa0cm was 14xa0m 3 /ha in mature (range 2–28xa0m 3 /ha), 22xa0m 3 /ha in overmature (7–38xa0m 3 /ha) and 111xa0m 3 /ha (70–184xa0m 3 /ha) in old-growth stands. Stand age and basal area of the cut stumps together explained over 70% of the variation in the volume of CWD. In old-growth forests, ca. 70% of the volume of CWD consisted of logs, 23% of intact dead standing trees and 7% of broken snags. Most of the volume of CWD belonged to the 20–29 and 30–39xa0cm diameter classes, but the mean proportion of large trunks ≥40xa0cm was also considerable, 24%. In managed forests man-made CWD, consisting of cut stumps, bolts and logging residues, accounted for an average of 25% of the total volume of CWD. In many cases most of the CWD volume belonged to the small diameter classes, 5–9 and 10–19xa0cm, and the mean proportion of large trunks was only 8%. We suggest that, considering the low proportion of both old-growth and overmature forests in southern Finland and the long time required for old-growth characteristics to develop, the most efficient short-term management strategy to increase structural diversity and old-growth attributes in managed forests would be to apply harvesting methods retaining the old-growth characteristics (i.e. large living trees, snags and logs) that already exist in overmature and mature stands.

Species richness of Coleoptera in mature managed and old-growth boreal forests in southern Finland

The beetle (Coleoptera) fauna of old-growth spruce (Picea abies) forest was compared with that from managed mature and overmature forests in southern Finland. Samples were collected from 9–11 sample plots in each case using 10 window-flight traps in each stand. These yielded a total of 43,289 beetles and 553 species of which 232 were associated with dead wood. The species richness of these saproxylic species was significantly higher in old-growth forests than in managed forests, and had very significant positive correlations with most dead-wood variables. Seventy eight percent of the saproxylic species were more abundant in old-growth than in mature managed forests, and their assemblages in managed and old-growth forests were distinctive with almost no overlap. On the other hand, species richness and assemblages of non-saproxylic species did not differ between the managed and old-growth forests. Obviously these species do not require as much attention as saproxylic species when conservation measures are planned in managed forests. An increase in the general level of decaying wood would improve the situation of many declining saproxylic species. Although the species richness of Coleoptera as a whole was higher in overmature than in mature managed stands, the value of long-rotation stands in preserving species assemblages typical of old-growth forests may be limited.

Dead trees left in clear-cuts benefit saproxylic Coleoptera adapted to natural disturbances in boreal forest

Forest management alters the pattern of forest dynamics from that in natural conditions in the boreal region. In order to examine how certain forestry measures matching natural dynamics affect forest insects, we compared assemblages of saproxylic Coleoptera on dead, standing birch trunks left behind in eight clear-cut areas with corresponding assemblages in seven mature forests in southern and eastern Finland. We used trunk-window traps for sampling. Distinct beetle assemblages were associated with the different habitats. Median numbers of species or specimens caught did not differ between closed forests and clear-cuts, but individual beetle species occurred unevenly among the habitats. Several beetle species associated with open forest habitat, e.g. burned forests or storm-damage areas, including species regarded as threatened in Finland, were found almost exclusively, in clear-cuts. Correspondingly, a number of beetle species occurring frequently in closed forests were not found in clear-cuts. We conclude that dead trunks left in the clear-cut areas may host not only generalist saproxylic species but also many beetle species specialized to warm, sun-exposed environments, and such species may not be able to survive in closed forests. Management measures matching suppressed natural disturbances are found useful in preserving diversity in managed forests.

Small-scale heterogeneity in the spatial distribution of carabid beetles in the southern Finnish taiga

Small-scale distribution of ground beetles (Cole- optera, Carabidae) was examined, based on catches among 300 pitfall traps, in a coniferous forest in southern Finland. The sample from the whole snow-free season comprised 2405 individuals of twenty-two species. Each of the most numerous species (Pterostichus oblongopunctatus (F.), Calathus micropterus (Dft.), Leistus terminatus (Hellw. in Pz.), Notiophilus biguttatus (F.) and Cychrus caraboides (L.)) was non-randomly distributed and formed aggrega- tions within the site of c. 1.3 ha in area. Although the five species occurred in every microhabitat defined in the plot, four of them (N. biguttatus was an exception) were more abundantly found in certain microhabitat types than in the others. In addition to vegetation around the traps, the numbers of Formica ants in the traps correlated with the numbers of carabids caught, mostly negatively. The consid- erable variation in catches and species richness among single traps and among blocks of 16 traps tended to even out, when larger subsamples were taken from the total pool (blocks of 48 traps). The distribution patterns observed within the plot were compared to a reference data set from similar habitat in the same region. Species distributions among microhabitats were slightly different in the reference set and the predic- tive success was relatively poor, probably due to different scales of study in the two data sets. Variation in species distribution in the two spatial scales studied (within a habitat patch and among them) is suppos- edly due to different factors. Although no direct evidence is available from our study area, we suggest that active micro- habitat selection explains the small-scale distribution within the study plot, whereas dynamics of local populations, influenced by regional-scale differences in habitat composi- tion, are the most likely explanation for the distribution pat- terns among habitat patches.

Bark beetles (Coleoptera, Scolytidae) and associated beetle species in mature managed and old-growth boreal forests in southern Finland

Abstract We compared the assemblages of bark beetles and associated beetle species among mature and overmature managed, and old-growth Picea abies (L.) Karst. dominated mesic forests in southern Finland. We established 10, 11 and 9 sample plots in these categories, respectively, within an area of 35xa0×xa080xa0km. We took the beetle samples by 10 window-flight traps in each 1xa0ha plot (total number of trapsxa0=xa0300). The species richness of bark beetles was highest in old-growth, lowest in mature, and intermediate in overmature forests. This was due to the greater amount and diversity of decaying wood in old-growth forests. Bark beetles which are dependent on deciduous trees, especially Trypodendron signatum (F.), were significantly more abundant in old-growth than in mature forests, obviously because deciduous trees have decreased in managed forests. The overall abundance of bark beetles was 23% higher in overmature and 30% higher in old-growth than in mature forests, but the differences were not statistically significant. Primary bark beetles comprised only 1% of the total catch, indicating that in non-epidemic conditions secondary scolytids are much more abundant than primary ones in old spruce forests. The abundance of bark beetles was best correlated with the amount of recently dead wood of the stand characteristics studied. Species associated with bark beetles showed patterns similar to those in bark beetles. The number of species was significantly higher in old-growth than in mature forests. The abundance of associated species was 61% higher in overmature and 89% higher in old-growth than in mature forests, although these differences were not statistically significant because of large inter-stand variation. It is thus likely that in the absence of major disturbances, the populations of primary bark beetles will stay at non-epidemic levels in old-growth forests. The species spectrum of bark beetles and their enemies could be broadened by promoting a deciduous mixture and improving the supply of dead trees in managed forests. This would also be beneficial to the conservation of species diversity in the managed forest landscape.

Colonisation of clearcut forests by ants in the southern Finnish taiga: a quantitative survey

We assessed the colonisation of clearcut forests by ants by using pitfall-trap data collected from clearcut areas of different age in southern Finland. We compared mature forests (age over 120 yr) with areas cleared 0, 2 and 10 yr before trapping. We concluded that the old-forest wood-ant systems are destroyed by clear-cutting, and that this is probably based on the loss of food resources. In the colonisation stage the role of stochasticity is counter-balanced by a number of deterministic species-specific factors in the succession of ant assemblages

Succession, Forest Fragmentation, and the Distribution of Wood Ants

I tested the hypothesis that the distribution of territorial wood-ant species (Formica rufa group) of different colony structure and dispersal strategy relate differently to the dynamics and landscape structure of boreal forests. Monogynous species (colonies have only one queen and inhabit one nest) that disperse through nuptial flight and subsequent temporary nest parasitism, should primarily be found in young forests and in smaller old-forest fragments. These long-distance dispersers can reach these areas where the nests of F. fusca group ants (which the wood-ant queens invade and parasitize) are more common, and these wood-ant colonies can monopolize the small fragments. Polygynous species (colonies have many queens) that disperse mainly through nest budding and may form large colonies of cooperative nests, should primarily be found in old forests and larger old-forest fragments. In such patches these short-distance dispersers have enough space for developing into strong colonies capable of ruling out all other territorial species. I mapped the nests of eight territorial ant species, three of which belonged to the wood-ant group, in fragmented forests of different age in southern Finland. In general, the mapping data supported my hypotheses. The monogynous F. lugubris was more common in young forests and in small old-forest fragments than expected by chance. The polygynous F. aquilonia was more common in old forests and in larger old-forest fragments.

Intensity of forest management and bark beetles in non-epidemic conditions: a comparison between Finnish and Russian Karelia

Abstract: The population levels of bark beetles in non‐epidemic conditions were compared between intensively managed forests in Finnish Karelia and extensively managed forests in Russian Karelia. Thirty randomly chosen sample plots with five window flight traps in each were established in both countries. The numbers of species and individuals of bark beetles did not differ between the countries. This indicates that extensive forest management has not increased the general level of bark beetle populations. Species assemblages were, however, different between the countries and between the forest site types. Hylastes brunneus and Pityogenes bidentatus, which are common in stumps or in logging residue of Scots pine, were more abundant in Finland. Crypturgus subcribrosus, Polygraphus punctifrons, and Hylurgops glabratus, which prefer dead spruce trees in shady conditions, and Trypodendron signatum, which live in dead deciduous trees, were more common in Russia. Bark beetles were most abundant in old mesic forests. The amount of decaying wood on the ground did not correlate with the numbers of bark beetles caught.

Effects of redispersal of seeds by ants on the vegetation pattern in a deciduous forest: a case study.

Abstract The floristic composition and distribution of mature plants, seedlings, and soil-seed material in both ant territories and territory borders between colonies of two ant species, Lasius fuliginosus and Formica polyctena , were compared in a deciduous forest in central Ukraine. Additional seed samples were taken from ant nests. Workers of both species collect seeds of myrmecochores, but only individuals of F. polyctena relocate seeds to territory borders after the removal of elaiosomes. Borders of F. polyctena territories are thus ‘garbage dumps’ of waste organic material and probably also nutrient-enriched microsites. The floristic composition of L. fuliginosus ’ territory differed from that of the territory borders and F. polyctena territory owing to a lower abundance of myrmecochores in the former. There were no great differences in the abundance or in the number of species (altogether fourteen species) in mature myrmecochores or non-myrmecochores among the sampling sites. However, the abundance and to some extent the number of species (altogether 21xa0species) of seedlings of myrmecochores (but not of non-myrmecochores) were lower in L. fuliginosus territory than in the other sampling sites. In particular, seedlings of two large-seeded myrmecochores, Asarum europaeum and Viola odorata , were more abundant in territory borders than in the territories. With a small-seeded myrmecochore, Ballota nigra , no such differences were found. Seeds of large-seeded myrmecochores, small-seeded myrmecochores and non-myrmecochores were more abundant than expected in the territory borders, in the nest of L. fuliginosus , in the nest of F. polyctena , respectively. It is suggested that seed flow from F. polyctena nests to the territory borders results in an increase in the seed-dispersal distances from the parent plant and among seeds dispersed in both small- and large-seeded myrmecochores. In large-seeded myrmecochores, this also results in a higher likelihood of reaching ‘garbage dumps’. The influence of ant behaviour on plant seed flow with different seed-dispersal strategies are discussed.

Distribution of mound-building ant species (Formica spp., Hymenoptera) in Finland : preliminary results of a national survey

In the first years data of the 10th Finnish National Forest Inventory (2005–2008) 533 active and 178 abandoned ant mounds were found yielding 4.2 mounds ha-1. We found 11 species: Formica rufa, F. polyctena, F. aquilonia, F. lugubris, F. pratensis, F. exsecta, F. fennica, F. pressilabris, F. forsslundi, F. suecica and F. uralensis. Five species occurred throughout the country, and four were restricted to the south. We found species-specific associations with either mineral soils or mires, with forest site type and with tree-canopy openness. Low fertility decreased the occurrence of polygynous species with large worker force, and sun-exposition was favourable for species with smaller colonies presumably because only large worker force enables metabolic thermoregulation of nests. Forest fragmentation and increased amount of edge habitats favourable for colony founding have presumably increased nest density whereas drainage of mires has reduced the amount of habitat of three species since the 1950s.